Axial-gap motor

ABSTRACT

An axial-gap motor comprising a base, a shaft, a stator frame, a plurality of electromagnet units, bearings, a rotor frame, and a plurality of permanent magnet units, an rotary encoder, and a drive unit. The rotor frame is spaced from the stator frame by a predetermined distance. The permanent magnet units oppose the electromagnet units across a predetermined axial gap. From the output of the rotary encoder, the drive unit supplies an excitation current to the electromagnet units, causing the magnetic poles of the units to repulse those of the permanent magnet units. The magnetic-field centerline that passes the center of each electromagnet unit intersects, at a predetermined angle, with the magnetic-field centerline that passes the center of one permanent magnet unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a Continuation Application of PCT Application No.PCT/JP03/01027, filed Jan. 31, 2003, which was not published under PCTArticle 21(2) in English, and which is based upon and claims the benefitof priority from the prior PCT Application No. PCT/JP02/00846, filedFeb. 1, 2002, the entire contents of the two PCT applications beingincorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an axial-gap motor in which therotor spaced from the stator, with an axial gap, is rotated by utilizingelectromagnetic repulsion.

[0004] 2. Description of the Related Art

[0005] Axial-gap motors are known, in which a gap exists in the axialdirection.

[0006] Many types of axial-gap motors have hitherto been manufactured,which have permanent magnet units and no brushes.

[0007] Such an electric motor can save energy because it has permanentmagnet units. Having no brushes, it is maintenance-free

[0008] In an electric motor of this type, the rotation torque isacquired usually from a rotating magnetic field generated between therotor and the stator. Hence, a rotating magnetic field should begenerated, though the motor has a permanent magnet unit. In view ofthis, a key to the energy saving in the electric motor is to reduce theenergy required to generate the turning magnetic field.

BRIEF SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide an axial-gapmotor that can save energy.

[0010] To attain the object, an axial-gap motor according to thisinvention comprises:

[0011] a stator frame;

[0012] a plurality of electromagnet units which are arranged on thestator frame;

[0013] a rotor frame which is spaced apart from the stator frame by apredetermined distance;

[0014] a plurality of permanent magnet units which are provided on therotor frame, which oppose the electromagnet units across an axial gapand each of which has a magnetic-field centerline that intersects with amagnetic-field centerline of the electromagnet unit as viewed in aradial direction;

[0015] a sensor unit which detects a positional relation of theelectromagnet units and permanent magnet units; and

[0016] a drive unit which detects, from an output of the sensor unit,that each of the permanent magnet units has rotated by a predeterminedangle from the position where magnetic poles of the permanent magnetunits substantially opposes magnetic poles of the electromagnet unitsand which supplies an excitation current to the electromagnet units, soas to repulse the magnetic poles of the permanent magnet units and themagnetic poles of the electromagnet units, through the predeterminedangle.

[0017] In the motor thus configured, the electromagnet units and thepermanent magnet units are so arranged that the magnetic-fieldcenterline of each electromagnet unit intersects with the magnetic-fieldcenterline of one permanent magnet unit, at the predetermined angle.Each permanent magnet unit is therefore rotated by a predetermined anglefrom the position where the magnetic poles of the permanent magnet unitssubstantially opposes that of the electromagnet units. The excitationcurrent is then supplied to the electromagnet units. The magnetic polesof the permanent magnet units repulse the magnetic poles of theelectromagnet units, through the predetermined angle.

[0018] In the axial-gap motor, when θ11+θ12+θ13)/number of poles of therotor=360°, the drive unit may preferably comprise means for supplyingthe excitation current to the electromagnet units in accordance with theoutput of the sensor unit such that θ11 is a period in which thepermanent magnet units remain close to the electromagnet units and theexcitation current is not supplied, θ12 is a period in which themagnetic fields of the electromagnet units repel the magnetic fields ofthe permanent magnet units and the excitation current is supplied, andθ13 is a period in which the excitation current is not supplied.

[0019] In the axial-gap motor described above, when θ21+θ22+θ23+θ24)/number of poles of the rotor=360°, the drive unit may preferablycomprise means for supplying the excitation current to the electromagnetunits in accordance with the output of the sensor unit such that θ21 isa period in which the permanent magnet units remain close to theelectromagnet units and the excitation current is not supplied, θ22 is aperiod in which the electromagnet units magnetically repulse thepermanent magnet units and the excitation current is supplied, θ23 is aperiod in which the excitation current is not supplied, and θ24 is aperiod in which the electromagnet units magnetically attract thepermanent magnet units and the excitation current is supplied.

[0020] In the axial-gap motor described above, each of the electromagnetunits may preferably has a magnetic-pole surface each which isorientated in an axial direction.

[0021] In the axial-gap motor described above, the electromagnet unitsmay preferably be arranged on the stator frame and spaced apart atregular intervals, irregular intervals, or regular and irregularintervals in a circumferential direction.

[0022] In the axial-gap motor described above, the electromagnet unitsmay preferably be arranged on the stator frame in one or more stages inthe radial direction.

[0023] In the axial-gap motor described above, each of the electromagnetunits may preferably comprise at least one of an I-shaped core and aU-shaped core and a coil wound around the at least one of the cores.

[0024] In the axial-gap motor described above, each of the electromagnetunits may preferably comprise a C-shaped yoke having a gap in which onepermanent magnet unit on the rotor frame is arranged, and coils woundaround the end portions of the yoke, respectively.

[0025] In the axial-gap motor described above, each of the electromagnetunits may preferably comprise a plurality of C-shaped yokes provided onone side of the stator frame and straddling one permanent magnet unit onthe rotor frame, a plurality of C-shaped yokes provided on the otherside of the rotor frame and straddling the permanent magnet unit on therotor frame, and coils wound around end portions of each of these yokes.

[0026] In the axial-gap motor described above, each of the electromagnetunits may preferably comprise a first yoke arranged on one side of thestator frame, straddling one permanent magnet unit on the rotor frameand having one end opposing the permanent magnet unit on the statorframe, and a second yoke arranged on the other side of the stator frame,straddling the permanent magnet unit on the rotor frame and having oneend opposing the permanent magnet unit on the stator frame.

[0027] In the axial-gap motor described above, the rotor frame maypreferably have a wall opposing the stator frame and a plurality ofgrooves made in the wall, extending in the radial direction and providedfor holding the permanent magnet units.

[0028] In the axial-gap motor described above, each of the permanentmagnet units may preferably have a magnetic-pole surface which isorientated in an axial direction.

[0029] In the axial-gap motor described above, the permanent magnets maypreferably be arranged on the rotor frame in a circumferentialdirection, with adjacent magnetic poles having the same polarity,different polarity or the same polarity and different polarities andspaced apart at regular intervals, irregular intervals or regular andirregular intervals.

[0030] In the axial-gap motor described above, the permanent magnets maybe preferably arranged on the rotor frame in a circumferential directionand in one or more stages, with adjacent magnetic poles having the samepolarity, different polarity or the same polarity and differentpolarities.

[0031] In the axial-gap motor described above, some of the permanentmagnet units are arranged on one wall of the rotor frame, which extendsin the axial direction, and the remaining permanent magnet units arearranged on the other wall of the rotor frame, which extends in theaxial direction.

[0032] In the axial-gap motor described above, each of the permanentmagnet units may preferably comprise a first permanent magnet piecearranged on one wall of the rotor frame, which extends in the axialdirection, a second permanent magnet piece arranged on the other wall ofthe rotor frame, which extends in the axial direction, and a thirdpermanent magnet piece arranged between the first and second permanentmagnet pieces.

[0033] The axial-gap motor described above, at least one part of therotor frame on which the permanent magnet units are provided is made oftitanium.

[0034] In the axial-gap motor described above, another rotor frame maybe provided on that side of the stator frame which faces away from therotor frame, and other electromagnet units may be arranged on the otherrotor frame and spaced apart from the permanent magnet units across apredetermined axial gap.

[0035] The axial-gap motor described above may preferably furthercomprise:

[0036] a shaft which is coupled to the rotor frame;

[0037] bearings which support the shaft; and

[0038] a base in which the bearing are provided.

[0039] In the axial-gap motor described above, a flywheel may preferablybe arranged on the rotor frame.

[0040] In the axial-gap motor described above, a mechanism maypreferably be provided to combine the rotor frame and the shaft togetherand separate the rotor frame and the shaft from each other.

[0041] In the axial-gap motor described above, a mechanism maypreferably be provided to combine the rotor frame and the shaft togetherand separate the rotor frame and the shaft from each other.

[0042] The axial-gap motor described above may further comprise agearbox that changes a rotational speed of the shaft.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0043]FIG. 1 is a sectional view showing an axial-gap motor that is anembodiment of this invention;

[0044]FIG. 2 is a perspective view of the embodiment;

[0045]FIG. 3 illustrates the stator section as viewed in the axialdirection;

[0046]FIG. 4 depicts the rotor section as viewed in the axial direction;

[0047]FIG. 5 is a diagram showing how the magnetic-field direction ofthe permanent magnet units on the rotor intersects with themagnetic-field direction of the electromagnet units on the stator;

[0048]FIG. 6 is a diagram of the electric circuit incorporated in theembodiment;

[0049]FIG. 7 is a circuit diagram showing the electromagnet units usedin the embodiment;

[0050]FIG. 8 is a diagram illustrating a method of exciting theelectromagnet units in the embodiment;

[0051]FIG. 9 is a waveform diagram showing the excitation currentssupplied to the four electromagnet units used in the embodiment;

[0052]FIG. 10 is a diagram illustrating another method of exciting theelectromagnet units in the embodiment;

[0053]FIG. 11 shows a stator section of another type for use in theembodiment, as viewed in the axial direction;

[0054]FIG. 12 depicts a rotor section of another type for use in theembodiment, as viewed in the axial direction;

[0055]FIG. 13 shows a stator section of still another type for use inthe embodiment, as viewed in the axial direction;

[0056]FIG. 14 shows a rotor section of still another type for use in theembodiment, as viewed in the axial direction;

[0057]FIG. 15 is a sectional view showing an axial-gap motor that isanother embodiment of this invention;

[0058]FIG. 16 depicts the stator section provided in the otherembodiment, as viewed in the axial direction;

[0059]FIGS. 17A to 17E show several types of electromagnet units for usein an axial-gap motor of this invention, each comprising an I-shapedcore or I-shaped cores;

[0060]FIGS. 18A and 18B show two types of electromagnet units for use inan axial-gap motor of this invention, each comprising a U-shaped core orU-shaped cores;

[0061]FIG. 19 is a sectional view showing an axial-gap motor that isstill another embodiment of this invention;

[0062]FIG. 20 shows an axial-gap motor that is another embodiment of theinvention, illustrating how the magnetic-field direction of thepermanent magnet units on the rotor intersects with the magnetic-fielddirection of the electromagnet units on the stator;

[0063]FIG. 21 is a sectional view depicting an axial-gap motor that isanother embodiment of the present invention;

[0064]FIG. 22 illustrates the stator section as viewed in the axialdirection;

[0065]FIG. 23 depicts the rotor section as viewed in the axialdirection;

[0066]FIG. 24 is a diagram showing an electromagnet unit used in theaxial-gap motor of this invention and having a C-shaped core;

[0067]FIG. 25 is a diagram shows how the magnetic-field direction of thepermanent magnet units on the rotor intersects with the magnetic-fielddirection of the electromagnet units on the stator;

[0068]FIG. 26 is a diagram depicts a permanent magnet unit on the rotor,which is different from the one illustrated in FIG. 24;

[0069]FIG. 27 is a diagram illustrating a yoke for use in theelectromagnet units, which is different from the one shown in FIG. 21;

[0070]FIG. 28 is a perspective view showing a part of the yokeillustrated in FIG. 27;

[0071]FIG. 29 is a diagram showing a yoke for use in the electromagnetunits, which is different from the one shown in FIG. 21;

[0072]FIG. 30 is a perspective view depicting a part of the yoke shownin FIG. FIG. 29; and

[0073]FIG. 31 is a perspective view showing another type of a rotorframe.

DETAILED DESCRIPTION OF THE INVENTION

[0074] Embodiments of the present invention will be described.

[0075]FIG. 1 is a sectional view showing an axial-gap motor according toan embodiment of this invention.

[0076] As FIG. 1 shows, the axial-gap motor according to the embodimenthas a stator and a rotor that oppose each other across an axial gap. Inthe electric motor, each electromagnet provided on the stator acts onthe same pole of the permanent magnet provide on the stator. Thus, anelectromagnetic repulsion develops. The repulsion rotates the rotor and,hence, the shaft.

[0077] The axial-gap motor according to the embodiment further has abase 10, bearings 11A and 11B, a stator frame 12, a rotor frame 13, ashaft 14, a plurality of permanent magnet units 18, and a plurality ofelectromagnet units 19. The stator frame 12 is provided on the base 10.The electromagnet units 19 are arranged on the stator frame 12. Thebearings 11A and 11B are provided in the base 10 and mounted on theshaft 14. The rotor frame 13 is mounted on the shaft 14, at midpoint inthe axial direction 300. The rotor frame 13 opposes the stator frame 12and can rotate. The permanent magnet units 18 are provided on the rotorframe 13. Each permanent magnet unit 18 opposes one electromagnet unit19 across an axial gap.

[0078] The axial-gap motor according to the embodiment further has arotary encoder 17 and a drive unit 22. The encoder 17 detects thepositional relation between each electromagnet unit 19 and one permanentmagnet unit 18. The drive unit 22 supplies an excitation current to theelectromagnet unit 19. The current is based on the output of the rotaryencoder 17.

[0079] In the motor thus constructed, the magnetic-field centerlinepassing the pole center of each electromagnet unit 19 on the statorintersects at, for example, 50° with the magnetic-field centerlinepassing the pole center of the permanent magnet unit 18 on the rotor.

[0080] The axial-gap motor according to this embodiment invention willbe described in detail, with reference to FIGS. 1 to 4.

[0081] As FIGS. 1 and 2 show, the axial-gap motor according to thisembodiment has the base 10. The base 10 comprises a first wall plate10A, a second wall plate 10B, and a bottom plate 10C. The second wall10B opposes the first wall plate 10A and spaced from the first wallplate 10A. The bottom plate 10C. connects one end of the first wallplate 10A to one end of the second wall plate 10B.

[0082] The base 10 may be a single casting or may be a three-piececomponent. In the latter case, it is made by welding the first wallplate 10A, second wall plate 10B and bottom plate 10C together orfastening them together with screws.

[0083] The stationary part of the bearing 11A is held in the other endportion of the first wall plate 10A. The stationary part of the bearing11B is held in the other end portion of the second wall plate 10A.

[0084] As FIG. 3 shows, the stator frame 12 has a hole 16. The statorframe 12 may be a single casting or may be made by processing a plate.

[0085] The shaft 14 passes through the rotating part of the bearing 11Aand also the rotating part of the bearing 11B. Note that the bearings11A and 11B are provided in the first wall plate 10A and the second wallplate 10B, respectively. The rotor frame 13 shown in FIG. 4 is fitted onthe shaft 14, at midpoint in the axial direction 300.

[0086] A screw is driven into the interface between the rotor frame 13and the shaft 14, fastening the frame 13 to the shaft 14.

[0087] The rotor frame 13 is thereby held, opposing the stator frame 12.

[0088] One end portion of the shaft 14 is the output shaft of theelectric motor. The disk 17A of the rotary encoder 17, i.e., sensorunit, is mounted on the other end portion of the shaft 14. The rotaryencoder 17 has a detecting section 17B, which is provided on the statorframe 12.

[0089] The rotary encoder 17 has a light-receiving/emitting element.This element is incorporated in the detecting section 17B. Thelight-receiving/emitting element detects slits or light-reflectingmembers provided in or on the disk 17A. The rotary encoder 17 outputs anelectric signal to a read line 17C.

[0090] The rotary encoder 17 can thus detect the positional relationbetween the electromagnet units 19, on the one hand, and the permanentmagnet unit 18, on the other. More specifically, it detects therotational position of the rotary frame 13 and the relative positions ofthe magnetic poles of the permanent magnet units 18 (18A, 18B, 18C and18D) provided on the rotor frame 13.

[0091] In the present embodiment, the permanent magnet units 18 areprovided on the rotor frame 13. More precisely, they are arranged in thecircumferential direction 302 and radial direction 301 such that onepole of each permanent magnet unit 18 is opposite in polarity to theadjacent pole of the next permanent magnet unit 18.

[0092] The sensor unit may not be an optical rotary encoder. It may be,for example, a Hall element. If this is the case, it can magneticallydetect the positions the permanent magnet units 18 take relative to theelectromagnet units 19.

[0093] As seen from FIG. 4, the rotary frame 13 is shaped like a disk.The rotary frame 13 can be a single casting or can be made by a plate.

[0094] The rotor frame 13 has grooves 15 in the side that opposes thestator frame 12. The grooves 15 are arranged in the circumferentialdirection at intervals of 90° (=360°/4). Each groove extends in theradial direction 301. The permanent magnet units 18 are held in thegrooves.

[0095] Thus, as FIG. 4 shows, four grooves 15 are made in the rotorframe 13 and arranged in the circumferential direction. And each groove15 extends in the radial direction 301.

[0096] The permanent magnet units 18 are held in the grooves 15. Theymay be secured to the rotor frame 13 by various methods, for example byusing screws or resin.

[0097] The grooves 15 made in the rotor frame 13 may be so shaped toprevent the permanent magnet unit 18 from slipping out.

[0098] A mechanism may be used to change the orientation of eachpermanent magnet unit 18 held in one groove 15. If changed inorientation, the permanent magnet units 18 will be so positioned toapply an electromagnetic repulsion effectively act in the electric motoraccording to this embodiment.

[0099] The permanent magnet units 18 held in the grooves 15 may differin shape. If so, the electromagnetic repulsion can effectively work inthe electric motor according to present embodiment.

[0100] A flywheel 21 is attached to the rotor frame 13. The flywheel 21contributes to smooth rotation of the rotor frame 13. It may not beused. Nevertheless, it should preferably be used if the number of polesis small.

[0101] The electromagnet units 19 (19A, 19B, 19C and 19D) are providedon the stator frame 12. The lead lines of the units 19 are let outwardsfrom the base 10.

[0102] As FIG. 5 shows, the magnetic-field centerline 200 of eachelectromagnet unit 19 intersects at angle θ with the magnetic-fieldcenterline 201 of the permanent magnet unit 18.

[0103] In this embodiment, the magnetic-field centerline of eachelectromagnet unit 19 is aligned with the axis of the shaft 14. Notethat “0” is the position where the magnetic fields of the permanentmagnet unit 18 and electromagnet unit 19 repel each other mosteffectively. The inventors hereof set 0 at, for example, 50°.

[0104] In the axial-gap motor of ordinary type, the rotor magnetic poleand the stator magnetic pole oppose each other. The embodiment ischaracterized in that the rotor magnetic pole and the stator magneticpole do not oppose each other.

[0105] The electric system of the axial-gap motor according to thisembodiment will be described with reference to FIGS. 6 to 9.

[0106]FIG. 6 is a circuit diagram of the axial-gap motor according tothis embodiment. The drive unit 22 has a switching section 22A. Thesection 22A outputs an excitation current. The excitation current drivesthe electromagnet units 19.

[0107] The switching section 22A is controlled by a switching controlsignal supplied from a control section 22B. The control section 22Breceives a signal from the rotary encoder 17.

[0108] The switching section 22A receives an AC current from an AC powersupply 23 and generates a direct current. The direct current is switchedor chopped. It is, thereby converted to an excitation current. Theexcitation current will be supplied to the electromagnet units 19.

[0109] The excitation current has a pulse waveform and a frequency of(360°/number of poles of the rotor)×2. This current is supplied to eachelectromagnet unit.

[0110] Four electromagnet units 19 are provided. Their coils areconnected as illustrated in FIG. 7.

[0111] The drive unit 22 is configured to perform two functions. First,it detects, from the output of the rotary encoder 17, that the permanentmagnet units 18 have rotated to angle θ1 from the positions where theirpoles oppose those of the electromagnet units 19. Second, it suppliesthe excitation current to the electromagnet units 19 such that the polesof the units 19 magnetically repel the poles of the permanent magnetunit 18 by angle θ2, from angle θ1.

[0112] More specifically, the drive unit 22 supplies the excitationcurrent to the electromagnet units 19 in accordance with the output ofthe rotary encoder 17. The excitation current has the frequency of 360°(=θ11+θ12+θ13)/number of poles of the rotor (=4, in this embodiment), asseen from FIG. 8. Here, θ11 is the period in which the electromagnetunits 19 are close to the permanent magnet units 18 and the excitationcurrent is not supplied to the units 19; θ12 is the period in which theexcitation current is supplied to the units 19 and the magnetic field ofeach unit 19 repels the magnetic field of the permanent magnet unit 18;and θ13 is the period in which the excitation current is not supplied tothe electromagnet units 19.

[0113] How the electromagnet units 19 are excited to rotate the rotor ina prescribed direction by 90° (=360°/4) will be described with referenceto FIG. 8.

[0114] In FIG. 8, angle 0° defines the position where each permanentmagnet unit 18 on the rotor lies most close to the electromagnet unit 19on the stator. At this position, the magnetic-field center of thepermanent magnet unit 18 and the magnetic-field center of theelectromagnet unit 19 are most close to each other.

[0115] The time when the magnetic-field centers of the units 18 and 19lie most close to each other is the starting point of the period θ11. Noexcitation current is supplied to the electromagnet unit 19 from thestarting point to ending point of the period θ11. In this period, themagnetic force of only the permanent magnet unit 18 attracts the core(i.e., magnetic member) of the electromagnet unit 19.

[0116] The excitation current is supplied to the electromagnet unit 19in the period θ12, or from the end of the period θ11, i.e., the startingpoint of the period θ12, to the end of the period 012.

[0117] Assume that the permanent magnet unit 18 is S pole. Then, themagnitude of the excitation current and the winding direction of thecoil of the unit 19 are so set that the unit 19 may be S pole, too. Themagnetic repulsion of the units 18 and 19 overcoming the magneticattraction developed while no excitation current is supplied to the unit19. It therefore rotates the permanent magnet 18 and the rotor frame 13in a prescribed direction.

[0118] Next, the permanent magnet unit 18 on the rotor and theelectromagnet unit 19 on the stator. No excitation current is suppliedto the electromagnet unit 19 in the period θ13, or from the end of theperiod θ11, i.e., the starting point of the period θ13, to the end ofthe period θ13. In this period, the inertia of the flywheel 21 rotatesthe permanent magnet unit 18 and the rotor frame 13 in the prescribeddirection.

[0119] In the above-described method of exciting the electromagnet units19, the polarity of each electromagnet unit 19 is inverted every timethe rotor rotates 90°. The permanent magnet units 18 and the rotor frame13 are thereby rotated continuously in the prescribed direction.

[0120] In the excitation method depicted in FIG. 8, θ11, θ12 and θ13are, for example, about 20°, about 20° and about 50°, respectively. Inthe period θ12 of applying the excitation current, the repulsion betweenthe electromagnet unit 19 and the permanent magnet unit 18 rotates therotor frame 13.

[0121]FIG. 9 shows when the timing of supplying the excitation currentto the electromagnet units 19A, 19B, 19C and 19D. The rotor frame 13 canbe rotated by electromagnetic repulsion, merely by supplying theexcitation current to each electromagnet unit 19 during only the periodθ12 that is a part of the time of 360°/number of rotor poles (i.e.,four, in this embodiment) arranged in the circumferential direction. Inaddition, energy can be greatly saved because the rotor comprisespermanent magnet units.

[0122] A method of exciting the electromagnet units 19, different fromthe method shown in FIG. 8, will be described with reference to FIG. 10.In the method of FIG. 8, each electromagnet unit 19 is excited so thatits the magnetic field repels the magnetic field of the permanent magnetunit 18, to rotate the rotor frame 13.

[0123] In the method of FIG. 10, electromagnetic repulsion andelectromagnetic attraction are applied to rotate the rotor frame 13. Theexcitation current is supplied to the electromagnet units 19 so thatθ21+θ22+θ23+θ24=360/number of rotor poles arranged in thecircumferential direction. Here, θ21 is the period in which the units 19remain close to the permanent magnet units 18 and the excitation currentis not supplied to the units 19; θ22 is the period in which theexcitation current is supplied to the units 19, achievingelectromagnetic repulsion; and θ23 is the period in which the excitationcurrent is not supplied to the units 19; and θ23 is the period in whichthe excitation current is supplied to the units 19, causingelectromagnetic attraction.

[0124] How the rotor is rotated by 90°=350°/4 (number of rotor poles) inthe method of FIG. 10 will be explained. In the electric motor to whichthis method is applied, the permanent magnet units 18 arrange in thecircumferential direction are alternately S pole and N pole.

[0125] In FIG. 10, the position where each permanent magnet unit 18 onthe rotor lies most close to the electromagnet unit 19 on the stator isdefined by angle 0°. At this position, the magnetic-field center of thepermanent magnet unit 18 and the magnetic-field center of theelectromagnet unit 19 are most close to each other. Assume that theperiod θ21 starts at this position. Then, no excitation current issupplied to the electromagnet units 19, from the starting point toending point of the period θ21. Therefore, only the magnetic force ofeach permanent magnet unit 18 attracts the core, or magnetic member, ofthe electromagnet unit 19.

[0126] The permanent magnet units 18 on the rotor and the electromagnetunit 19 on the stator. From the start point of the period θ22, or theend of the period θ21, to the ending point of the period θ22, theexcitation current is supplied to the electromagnet units 19.

[0127] Assume that the permanent magnet unit 18 are S poles. Themagnitude of the excitation current and the winding direction of thecoils of the units 19 are so set that the units 19 may be S pole, too.

[0128] Since the permanent magnet units 18 and the electromagnet units19 are S poles, each permanent magnet unit 18 repels the opposingpermanent magnet unit 18. The magnetic repulsion rotates the permanentmagnets 18 and the rotor frame 13 in a prescribed direction. This isbecause the repulsion overcomes the magnetic attraction developed whileno excitation current is supplied to the units 19.

[0129] Next, the permanent magnet unit 18 on the rotor and theelectromagnet unit 19 on the stator. No excitation current is suppliedto the electromagnet unit 19 in the period θ23, or from the end of theperiod θ21, i.e., the starting point of the period θ13, to the end ofthe period θ23. In this period, the inertia of the flywheel 21 rotatesthe permanent magnet unit 18 and the rotor frame 13 in the prescribeddirection.

[0130] The permanent magnet unit 18 on the rotor and the electromagnetunit 19 on the stator. In the period θ24, that is, from the ending pointof the period θ23, i.e., the starting point of the period θ24, to theending point of the period θ24, the excitation current is supplied tothe electromagnet units 19.

[0131] In this period, the next permanent magnet unit 18 and the nextelectromagnet unit 19 are an S pole and an N pole, respectively. Thus,electromagnetic attraction acts on the permanent magnet unit 18,rotating the permanent magnet unit 18 and the rotor frame 13 in theprescribed direction.

[0132] This excitation method is applied to each electromagnet unit 19,while changing the polarity thereof every 90°. It is therefore possibleto rotate the permanent magnet units 18 and the rotor frame 13continuously in one direction.

[0133] This excitation method can rotate the rotor frame 13 by virtue ofelectromagnetic repulsion and electromagnetic attraction, if theexcitation current is supplied in only the period θ24 to achieveelectromagnetic attraction.

[0134] In the excitation method of FIG. 10, θ21, θ22, θ23 and θ24 are,for example, 20°, 20°, 30° and 20°, respectively.

[0135] In the present invention, the electromagnet units are arranged onthe stator frame in the radial direction, in one or more stages.

[0136] How the electromagnet units may be arranged in the embodimentdescribed above will be explained. In this invention, the electromagnetunits are arranged on the stator frame in the circumferential direction,spaced apart at equal distance or different distances, or some at equaldistance and the others at different distances.

[0137] A case where the permanent magnet units are arranged in thecircumferential direction will be described.

[0138] In the invention, the permanent magnet unit is arranged on therotor frame in the circumferential direction, spaced apart at equaldistance or different distances, or some at equal distance and theothers at different distances. Thus, any two adjacent units may be ofthe same polarity or opposite polarities, or some units may have onepolarity, while the others have the other polarity.

[0139] The permanent magnet units are arranged in the circumferentialdirection and also in the radial direction in one or more stages. Thus,any two adjacent units are of the same polarity or the oppositepolarities, or some units have one polarity and the others have theopposite polarity.

[0140] A stator which differs in structure from the one described abovewill be described, with reference to FIG. 11. As FIG. 11 shows,electromagnet units 19A, 19B and 19C are arranged in one stage and inthe circumferential direction at regular intervals of 120°.

[0141] If the stator having this structure is employed, the period ofsupplying no excitation current and the period of supplying theexcitation current are set, each for the 120°-rotation of the stator.

[0142] A rotor which differs in structure from the one described abovewill be described, with reference to FIG. 12. As FIG. 12 illustrates,permanent magnet units 18 (18A and 18B) are arranged in grooves 15,spaced apart by 180° in the circumferential direction. The adjacentpoles of the units 18 are of the opposite polarities.

[0143] If this rotor is employed, the period of supplying no excitationcurrent and the period of supplying the excitation current are set, eachfor the 180°-rotation of the stator, unlike in the case illustrated inFIGS. 8 to 10.

[0144] Another stator that differs in structure from the one describedabove will be described, with reference to FIG. 13. As FIG. 13 depicts,this stator has electromagnet units 19 (19A, 19B, 19C, 19D, 19E, 19F,19G and 19H). The units 19 are arranged on the stator frame 12 in twostages in the radial direction. The four pairs of electromagnet units 19are arranged in the circumferential direction at intervals of 90°.

[0145] The pair of electromagnet units 19A and 19E, the pair ofelectromagnet units 19B and 19F, the pair of electromagnet units 19C and19G, and the pair of electromagnet units 19D and 19H are considered tocorrespond to the electromagnet units 19A, 19B, 19C and 19D shown inFIG. 3. Thus, the period of supplying no excitation current and theperiod of supplying the excitation current are set, each for the90′-rotation of the stator, in the same way as in the case shown inFIGS. 8 to 10.

[0146] If the electromagnet units do not form four pairs, thecurrent-supplying mode will of course differ from the mode shown inFIGS. 8 to 10. The period of supplying no excitation current and theperiod of supplying the excitation current will be set, each for the90°-rotation of the stator.

[0147] Another rotor, which differs in structure from the one describedabove, will be described, with reference to FIG. 14. As FIG. 14 shows,permanent magnet units 18 (18A, 18B, 18C, 18D, 18F, 18G and 18H) arearranged in grooves 15. They are spaced apart by 90° in thecircumferential direction. These units 18 are arranged in two states inthe radial direction. The adjacent poles of the units 18 are of theopposite polarities.

[0148] The pair of permanent magnet units 18A and 18E, the pair ofpermanent magnet units 18B and 18F, the pair of permanent magnet units18C and 18G, and the pair of permanent magnet units 18D and 18H areconsidered to correspond to the permanent magnet units 18A, 18B, 18C and18D shown in FIG. 3. Thus, the period of supplying no excitation currentand the period of supplying the excitation current are set, each for the90′-rotation of the rotor, in the same way as in the case shown in FIGS.8 to 10. If the permanent magnet units do not form four pairs, thecurrent-supplying mode will, of course, differ from the mode shown inFIGS. 8 to 10. The period of supplying no excitation current and theperiod of supplying the excitation current will be set, each for the90′-rotation of the rotor.

[0149] Another embodiment of an axial-gap motor according to thisinvention, which differs from the one shown in FIG. 1, will be describedbelow with reference to FIGS. 15 and 16. The components identical tothose shown in FIG. 1 are designated at the same reference numerals.

[0150] As seen from FIG. 15, the axial-gap motor according to thisembodiment has a base 10. The base 10 comprises a first wall plate 10A,a second wall plate 10B, and a bottom plate 10C. The second wall 10Bopposes the first wall plate 10A and spaced from the first wall plate10A. The bottom plate 10C connects one end of the first wall plate 10Ato one end of the second wall plate 10B.

[0151] The base 10 may be a single casting or may be a three-piececomponent. In the latter case, it is made by welding the first wallplate 10A, second wall plate 10B and bottom plate 10C together orfastening them together with screws.

[0152] The stationary part of the bearing 11A is held in the other endportion of the first wall plate 10A. The stationary part of the bearing11B is held in the other end portion of the second wall plate 10A.

[0153] As FIG. 16 shows, the stator frame 12′ has a hole 16 made in thecenter part. It also has four holes 16A. A shaft 14 passes through thehole 16. The four holes 16A are made in the stator frame 12′. They arearranged in one stage in the radial direction and spaced apart atintervals of 90° in the circumferential direction. The stator frame 12′can be a single casting or can be made by processing a plate. Note thatthe stator frame 12′ lies between two rotor frames 13 and 13′.

[0154] The electric motor has electromagnet units 101, which may be ofthe type shown in FIG. 17B. The unit 101 shown in FIG. 17B comprises anI-shaped core 111 and a coil 120 wound around the core 111. The ends ofthe I-shaped core 111 are used as magnetic poles.

[0155] The shaft 14 passes through the rotary part of the bearing 11Aheld in the first wall plate 10A and through the rotary part of thebearing 11B held in the second wall plate 10B.

[0156] The rotor frame 13 and 13′, which are similar to each other, aremounted on the shaft 14. The frames 13 and 13′ are spaced apart in theaxial direction 300, with the stator frame 12′ located between them. Ascrew 20 is driven into the interface between the frame 13 and the shaft14, securing the rotor frame 13 to the shaft 14. Similarly, a screw 20′is driven into the interface between the frame 13′ and the shaft 14,fastening the rotor frame 13′ to the shaft 14.

[0157] Thus, the rotor frames 13 and 13′ oppose the stator frame 12,across axial gaps.

[0158] One end of the shaft 14 is the output shaft of the electricmotor, as in the embodiment of FIG. 1. A rotary encoder 17, which is asensor unit, is mounted on the other end of the shaft 14.

[0159] The rotary encoder 17 can detect the positional relation betweenthe permanent electromagnet units 18 provided on the rotor frame 13, thepermanent electromagnet units provided on the rotor frame 13′, and theelectromagnet units 19. More specifically, it detects the rotationalpositions of the rotary frames 13 and 13′, and hence the relativepositions of the magnetic poles of the permanent magnet units 18provided on the rotor frames 13 and 13′.

[0160] In this embodiment, the permanent magnet units 18 provided on therotor frames 13 and 13′, are arranged in the circumferential direction302 and radial direction 301. They are so arranged that each has its onepole opposite in polarity to the adjacent pole of the next permanentmagnet unit 18.

[0161] Flywheels 21 and 21′ are attached to the rotor frames 13 and 13′.The flywheels 21 and 21′ contribute to smooth rotation of the rotorframes. They may not be used. Nevertheless, they should better be usedif the number of poles is small, in order to make the rotor framesrotate smoothly.

[0162] The magnetic-field centerline 200 of each electromagnet unit 19intersects at angle θ with the magnetic-field centerline 201 of thepermanent magnet unit 18.

[0163] In the present embodiment, the magnetic-field centerline of eachelectromagnet unit 19 aligns with the axis of the shaft 14. Note that“θ” is the position where the magnetic fields of the permanent magnetunit 18 and electromagnet unit 19 repel each other effectively. Theinventors hereof set θ at, for example, 50°, as in the embodiment ofFIG. 1.

[0164] In this embodiment, the rotor magnetic pole and the statormagnetic pole do not oppose each other and two rotors oppose each other,with one stator located between them. The electromagnet units 19 on thestator and the permanent magnet units on the two rotors cooperate toapply an electromagnetic force to the rotor efficiently. The embodimentcan therefore be a high-efficiency electric motor.

[0165] Various electromagnet units that can be used in the embodimentsdescribed above will be described in detail, with reference to FIGS. 17Ato 17E and FIGS. 18A and 18B.

[0166] The electromagnet unit 100 shown in FIG. 17A comprises anI-shaped core 110 and a coil 120 wound around the core 110. One end ofthe I-shaped core 110 is used as a magnetic pole. This electromagnetunit 100 can be used in the configuration of FIG. 1.

[0167] The electromagnet unit 101 shown in FIG. 17B comprises anI-shaped core 111 and a coil 120 wound around the core 111. The ends ofthe I-shaped core 110 are used as magnetic poles. The electromagnet unit101 can be used in the configuration of FIG. 15.

[0168] The electromagnet unit 102 shown in FIG. 17C comprises twoI-shaped cores 110 and two coils 120 wound around the cores 110,respectively. One end of the first I-shaped core 110 and one end of thesecond I-shaped core 110 are used as magnetic poles. These magneticpoles are opposite in polarity.

[0169] The electromagnet unit 103 shown in FIG. 17D comprises twoI-shaped cores 110 and two coils 120 wound around the cores 110,respectively. One end of the first I-shaped core 110 and one end of thesecond I-shaped core 110 are used as magnetic poles. The magnetic poleshave the same polarity.

[0170] The electromagnet unit 104 shown in FIG. 17E comprises twoI-shaped cores 111 and two coils 120 wound around the cores 111,respectively. The ends of each I-shaped core 111 are used as magneticpoles.

[0171] The electromagnet unit 105 shown in FIG. 18A comprises a U-shapedcore 112 and a coil 120 wound around the core 112. The ends of theU-shaped core 112 are used as magnetic poles.

[0172] The electromagnet unit 106 shown in FIG. 18B comprises twoU-shaped cores 112 and two coils 120 wound around the cores 112,respectively. The ends of each U-shaped core 112 are used as magneticpoles.

[0173]FIG. 19 shows an axial-gap motor in which a gearbox 24 coupled tothe shaft 14 of the type shown in FIG. 1. This motor can provide agreater torque than the shaft 14.

[0174] The axial-gap motor of this embodiment has two rotation systems.The first system is concerned with the rotation of the rotor frame 13.The second system is concerned with the rotation of the output shaft 24Aof the gearbox 24.

[0175] Fins may be provided on the rotor frame 13. If so, the rotorframe 13 will work as a high-speed, low-torque fan mechanism, and theoutput shaft 24A of the gearbox 24 will provide a low-speed, high-torquerotation mechanism.

[0176] In this embodiment, the magnetic-field centerline of eachelectromagnet unit 19 on the stator ant the magnetic-field centerline ofthe permanent magnet unit 18 on the rotor intersect at, for example,50°. More precisely, the magnetic-field centerline that passes themagnetic pole center of the electromagnet unit 19 provided on the statorextends in the axial direction of the shaft 14.

[0177] With reference to FIG. 20 an axial-gap motor will be described,in which the magnetic-field centerline that passes the magnetic polecenter of each permanent magnet unit 18 on the rotor extends in theaxial direction of the shaft 14.

[0178] As FIG. 20 shows, grooves 15′ are made in the rotor frame 13. Inthe grooves 15′, permanent magnet units 18 are held. The magnetic-fieldcenterline 201, which passes the magnetic pole center of each permanentmagnet unit 18, extends in the axial direction of the shaft 14.

[0179] Electromagnet units 19 are secured to the stator frame such thatthe magnetic-field centerline 200 of each unit 19 intersects with themagnetic-field centerline 201 that passes the magnetic pole center ofthe permanent magnet unit 18.

[0180] This configuration can be applied to the electric motorsillustrated in FIGS. 1 to 19, to attain the same advantages as theelectric motors shown in FIGS. 1 to 19.

[0181] An axial-gap motor, which is another embodiment of the inventionand differs from those shown in FIGS. 1, 15 and 19, will be describedwith reference to FIGS. 21 to 25.

[0182]FIG. 21 is a sectional view depicting an axial-gap motor that isanother embodiment of the present invention.

[0183] The axial-gap motor according to this embodiment has a base 410.The base 410 comprises a first wall plate 410A, a second wall plate410B, a third wall plate 410C, a fourth wall plate 410D, and a bottomplate 410E. The second wall 410B opposes the first wall plate 410A andspaced from the first wall plate 410A. The third wall plate 410C liesbetween the first and second wall plates 410A and 410G and opposes thefirst wall plate 410A. The fourth wall plate 410D opposes the secondwall plate 410B. The bottom plate 410E connects the lower ends of thefirst, second, third and fourth wall plates 410A, 410B, 410C and 410D toone another.

[0184] The base 410 may be a single casting or may be a five-piececomponent. In the latter case, it is made by welding the first wallplate 410A, second wall plate 410B, third wall plate 410C and fourthwall plate 410D and the bottom plate 410E together or fastening themtogether with screws.

[0185] The stationary part of the bearing 411A is held in the other endportion of the first wall plate 410A. The stationary part of the bearing411B is held in the other end portion of the second wall plate 410A. Thethird and fourth wall plates 410C and 410D have a hole each. A shaft 14passes through the holes made in the wall plates 410C and 410D.

[0186] A stator frame 412 is provided between the third wall plate 410Cand the fourth wall plate 410D and secured thereto by means of screws.The stator frame 412 comprises a support section 412A and end plates412B and 412C. The support section 412A supports the yokes 419 ofelectromagnet units 418, which will be described later in detail. Theend plates 412B and 412C have a hole each in the center part. The shaft14 passes through the holes of the end plates 412B and 412C. The supportsection 412A may be a single casting or may be a three-piece component.In the latter case, it is made by welding the support section 412A andthe end plates 412B and 412C together or fastening them together withscrews.

[0187] As FIG. 21 shows, the shaft 414 passes through the rotary part ofthe bearing 411A held in the first wall plate 410A and through therotary part of the bearing 411B held in the second wall plate 410B. Theshaft 414 passes through the holes made in the third and fourth wallplates 410D and 410D, too.

[0188] As FIG. 21 shows, too, a rotor frame 413 is provided between thethird and fourth wall plates 410C and 410D. A fastening member 414Asecures the rotor frame 413 to the shaft 414. The rotor frame 413contains permanent magnet units 416 (not shown in FIG. 21). The rotorframe 413 can be made, in part or in entirety, of titanium that isremarkably nonmagnetic metal. If the rotor frame 413 is made of titaniumpartly or entirely, the magnetic fluxes of the permanent magnet units416 will leak but a little and will effectively act on the electromagnetunits 418. Thus, the magnetic fluxes will contribute much to generationof rotation moment.

[0189] One end of the shaft 414 is the output shaft of the electricmotor. The disc 417A of a rotary encoder 417, which is a sensor unit, ismounted on the other end of the shaft 414.

[0190] The rotary encoder 417 has a detecting section 417B. Thedetecting section 417B is attached to the first wall plate 410A. Therotary encoder 417 is designed to detect the positional relation betweenthe permanent magnet units 418, on the one hand, and the electromagnetunits 416, on the other. The rotary encoder 417 has alight-receiving/emitting element, which is incorporated in the detectingsection 417B. The light-receiving/emitting element detects slits orlight-reflecting members provided in or on the disk 417A. The rotaryencoder 417 outputs an electric signal to a read line 417C. The sensorunit may be other than the optical rotary encoder. It may be, forexample, a Hall element. If this is the case, the sensor unit canmagnetically detect the positions the permanent magnet units 416 takerelative to the electromagnet units 418.

[0191] In this embodiment, four permanent magnet units 416 are providedin each side of the rotor frame 413, which opposes the electromagnetunits 413. They are arranged in the circumferential direction atintervals of 90° (=360°/4). More precisely, as illustrated in FIG. 22that shows one side of he rotor frame 413, grooves 415 are made in eachside of the rotor frame 413. Diamond-shaped permanent magnets, forexample, are held in the grooves 415.

[0192] Note that the permanent magnet units 416 are arranged on thesides of the rotary frame 413 such that any two adjacent units on eachside or both sides are of the same polarity or the opposite polarities.

[0193] As mentioned above, the permanent magnet units 416 are held inthe grooves 415. They may be secured to the rotor frame 413 by variousmethods, for example by using screws or resin.

[0194] The grooves 415 made in the rotor frame 413 may be so shaped toembed the permanent magnet unit 416 completely, thus preventing the samefrom slipping out.

[0195] A mechanism may be used to change the orientation of eachpermanent magnet unit 416 held in one groove 415. If so changed inorientation, the permanent magnet units 416 will take such positionsthat an electromagnetic repulsion will effectively act in the electricmotor according to the present embodiment.

[0196] The permanent magnet units 18 held in the grooves 15 may differin shape. In this case, the electromagnetic repulsion can effectivelywork in the electric motor according to present embodiment.

[0197] In this embodiment, two sets of electromagnet units 418 areprovided in the stator frame 412. Each set consists of four units 418that are arranged in the circumferential direction at intervals of 90°(=360°/4). To be more specific, four electromagnet units 418 are sopositioned that their magnetic poles oppose the permanent magnet units416 provided on the rotor frame 413, as seen from FIG. 23 that shows oneside of the stator frame 412. As FIGS. 21 and 24 depict, any twoelectromagnet units 418 opposing across the stator frame 412 comprise aC-shaped yoke 419 and two coils 420. The yoke 491 has a gap in which onepermanent magnet unit 416 may lie. The coils 420 are wound around theend portions of the yoke 419, respectively.

[0198] The positional relation between the permanent magnet units 416 onthe rotor, on the one hand, and the electromagnet units 418 on thestator, on the other hand, will be described with reference to FIG. 25.As FIG. 25 shows, the magnetic-field centerline of any permanent magnetunit 416 provided on the stator intersects at angle θ with themagnetic-field centerline of one electromagnet unit 418.

[0199] In this case, the magnetic-field centerlines of electromagnetunits 418A1 and 418A2 align with the axis of the shaft 414. Note that“θ” is the position where the magnetic fields of the permanent magnetunit 416 and electromagnet unit 418 repel each other effectively. Theinventors hereof set θ at, for example, 50°.

[0200] The electric circuit incorporated in the axial-gap motoraccording to this embodiment is the same as the circuit illustrated inFIG. 6. The excitation current supplied to the electromagnet units 418are identical to the current used in the circuit of FIG. 6. Theexcitation current has a pulse waveform and a frequency of (360°/numberof poles of the rotor). This current is supplied to each electromagnetunit.

[0201] In the axial-gap motor according to this embodiment, theelectromagnet units 418 and the permanent magnet units 416 are arrangedso that the magnetic-field centerline of each electromagnet unit mayintersects at angle θ with that of the corresponding permanent magnetunit 416. And the excitation current is supplied to the electromagnetunit 418 to make the unit 418 magnetically repels the permanent magnetunit 416, rotating the unit 416 by a certain angle from the positionwhere its magnetic pole opposes that of the electromagnet unit 416 andfurther by a prescribed.

[0202] The rotor frame 413 holding the permanent magnet units 416 liesin the gap between two sets of electromagnet units 418, each having twomagnetic poles that are opposite in polarity. Hence, the magnetic forceof each permanent magnet unit 416 and that of the electromagnet unit 418efficiently repel each other. The embodiment can therefore be ahigh-efficiency electric motor.

[0203] A modified rotor section will be described with reference to FIG.26. In FIG. 26, the components identical to those shown in FIG. 25 aredesignated at the same reference numerals. As FIG. 26 shows, the rotorframe 413 has grooves 415′. In the grooves 415′, permanent magnet units421 are arranged in the axial direction, too.

[0204] The permanent magnet units 421 and the permanent magnet units 416on both sides of the rotor frame 413 constitute magnetic paths. Thismakes the magnetic force of the rotor frame 413 effectively act on theelectromagnet units 418 provided on the stator. This embodiment cantherefore be a high-efficiency electric motor.

[0205] Electromagnet units of another type will be described withreference to FIGS. 27 to 30.

[0206]FIG. 27 shows two electromagnet units, and FIG. 28 shows one ofthem. Each unit comprises four coils 420 and two C-shaped yokes 422 and423 each having two magnetic poles. Two coils 420 are wound around themagnetic poles of one yoke 422. Similarly, two coils 420 are woundaround the magnetic poles of the other yoke 423. The two electromagnetunits are arranged on the sides of the rotor frame 413, respectively,such that the magnetic poles of one unit oppose those of the other unit.

[0207]FIG. 29 shows two electromagnet units, and FIG. 30 shows one ofthem. Each electromagnet unit comprises four coils 420 and one yoke 424having four magnetic poles. Four coils 420 are wound around the fourmagnetic poles of the yoke 424. The two electromagnet units are arrangedon the sides of the rotor frame 413, respectively, such that themagnetic poles of one unit oppose those of the other unit.

[0208] The electromagnet units of FIGS. 27 and 28 can constitute amagnetic circuit from which magnetism scarcely leaks. So can theelectromagnetic units of FIGS. 29 and 30. These electromagnetic unitsserve to provide high-efficiency electric motors.

[0209] A rotor frame 425 and permanent magnet units 426, different fromthose described thus far, will be described with reference to FIG. 31.

[0210] As FIG. 31 depicts, the rotor frame 425 comprises a rotor bar425A and U-shaped parts formed integral with the ends of the bar 425A.The rotor bar 425A has a hole made in the middle part. The hole allowspassage of a shaft (not shown). Each U-shaped part comprises two legs425B and 425C. The legs 425B and 425C have a groove 425E each, made inthat side which opposes an electromagnet unit (not shown). Two permanentmagnet units 426 are held in the grooves 425E of each U-shaped part.

[0211] The electromagnet units and the permanent magnet units 426, allshown in FIG. 31, are secured in the same manner as those shown in FIGS.25 and 26. The grooves 425E may have any shape that is desirable in viewof the shape of the permanent magnet units 426. The units 426 may besecured to the rotor frame 425 by various methods, for example by usingscrews or resin.

[0212] Thus constructed, the rotor frame 425 can help to provide alightweight two-pole rotor.

[0213] The present invention is not limited to the embodiments describedabove. Various changes and modifications can be made without departingfrom the scope and spirit of the invention.

[0214] With regard to the permanent magnet units on the rotor, thenumber of poles they have and the arrangement of the poles in thecircumferential and radial direction can be selected on the basis of thenumber of poles provided on the stator and the like.

[0215] With regard to the electromagnet units on the stator, the numberof poles they have and the arrangement of the poles in thecircumferential and radial direction can be selected on the basis of thenumber of poles provided on the rotor and the like.

[0216] The permanent magnet units and electromagnet units can havevarious structures and shapes. The coils can be connected in variousways, provided that they generate such magnetic repulsion and attractionas desired in the present invention.

[0217] Further, the above-described embodiments may be combined inwhichever way possible. Any combination of the embodiments can attainthe advantages of the embodiments.

[0218] Moreover, the embodiments include various phases of theinvention. The components disclosed herein may be combined in variousways to make various inventions.

[0219] For example, an invention may be made if some components of anyembodiment described above are not used. In this case, the knowntechniques shall be employed to make up for the components not used.

[0220] As indicated above, the present invention provides an axial-gapmotor that comprises:

[0221] a stator frame;

[0222] a plurality of electromagnet units which are arranged on thestator frame;

[0223] a rotor frame which is spaced apart from the stator frame by apredetermined distance;

[0224] a plurality of permanent magnet units which are provided on therotor frame, which oppose the electromagnet units across an axial gapand each of which has a magnetic-field centerline that intersects with amagnetic-field centerline of the electromagnet unit as viewed in aradial direction;

[0225] a sensor unit which detects a positional relation of theelectromagnet units and permanent magnet units; and

[0226] a drive unit which detects, from an output of the sensor unit,that each of the permanent magnet units has rotated by a predeterminedangle from the position where magnetic poles of the permanent magnetunits substantially opposes magnetic poles of the electromagnet unitsand which supplies an excitation current to the electromagnet units, soas to repulse the magnetic poles of the permanent magnet units and themagnetic poles of the electromagnet units to repel and rotate thepermanent magnet units, through the predetermined prescribed angle.

[0227] In the electric motor thus configured, the electromagnet unitsand the permanent magnet units are so arranged that the magnetic-fieldcenterline of each electromagnet unit intersects at the predeterminedangle with the magnetic-field centerline of one permanent magnet unit.Hence, each permanent magnet unit is rotated by a predetermined anglefrom the position where the magnetic poles of the permanent magnet unitssubstantially opposes that of the electromagnet units. The excitationcurrent is then supplied to the electromagnet units. The magnetic polesof the electromagnet units therefore repel and rotate the permanentmagnet units through a prescribed angle.

[0228] With the present invention it is therefore possible to rotate thepermanent magnet units and the rotor frame with a current smaller thanotherwise. The invention can provide an axial-gap motor that has goodcharacteristics in view of energy saving.

What is claimed is:
 1. An axial-gap motor comprising: a stator frame; aplurality of electromagnet units which are arranged on the stator frame;a rotor frame which is spaced apart from the stator frame by apredetermined distance; a plurality of permanent magnet units which areprovided on the rotor frame, which oppose the electromagnet units acrossan axial gap and each of which has a magnetic-field centerline thatintersects with a magnetic-field centerline of the electromagnet unit asviewed in a radial direction; a sensor unit which detects a positionalrelation of the electromagnet units and permanent magnet units; and adrive unit which detects, from an output of the sensor unit, that eachof the permanent magnet units has rotated by a predetermined angle fromthe position where magnetic poles of the permanent magnet unitssubstantially opposes magnetic poles of the electromagnet units andwhich supplies an excitation current to the electromagnet units, so asto repulse the magnetic poles of the permanent magnet units and themagnetic poles of the electromagnet units, through the predeterminedangle.
 2. The axial-gap motor according to claim 1, whereinθ11+θ12+θ13)/number of poles of the rotor=360°, the drive unit comprisesmeans for supplying the excitation current to the electromagnet units inaccordance with the output of the sensor unit such that θ11 is a periodin which the permanent magnet units remain close to the electromagnetunits and the excitation current is not supplied, θ12 is a period inwhich the magnetic fields of the electromagnet units repel the magneticfields of the permanent magnet units and the excitation current issupplied, and θ13 is a period in which the excitation current is notsupplied.
 3. The axial-gap motor according to claim 1, whereinθ21+θ22+θ23+θ24)/number of poles of the rotor=360°, the drive unitcomprises means for supplying the excitation current to theelectromagnet units in accordance with the output of the sensor unitsuch that θ21 is a period in which the permanent magnet units remainclose to the electromagnet units and the excitation current is notsupplied, θ22 is a period in which the electromagnet units magneticallyrepel the permanent magnet units and the excitation current is supplied,θ23 is a period in which the excitation current is not supplied, and θ24is a period in which the electromagnet units magnetically attract thepermanent magnet units and the excitation current is supplied.
 4. Theaxial-gap motor according to claim 1, wherein each of the electromagnetunits has a magnetic-pole surface each which is orientated in an axialdirection.
 5. The axial-gap motor according to claim 1, wherein theelectromagnet units are arranged on the stator frame and spaced apart atregular intervals, irregular intervals, or regular and irregularintervals in a circumferential direction.
 6. The axial-gap motoraccording to claim 1, wherein the electromagnet units are arranged onthe stator frame in one or more stages in the radial direction.
 7. Theaxial-gap motor according to claim 1, wherein each of the electromagnetunits comprises at least one of an I-shaped core and a U-shaped core anda coil wound around said at least one of the cores.
 8. The axial-gapmotor according to claim 1, wherein each of the electromagnet unitscomprises a C-shaped yoke having a gap in which one permanent magnetunit on the rotor frame is arranged, and coils wound around the endportions of the yoke, respectively.
 9. The axial-gap motor according toclaim 1, wherein each of the electromagnet units comprises a pluralityof C-shaped yokes provided on one side of the stator frame andstraddling one permanent magnet unit on the rotor frame, a plurality ofC-shaped yokes provided on the other side of the rotor frame andstraddling the permanent magnet unit on the rotor frame, and coils woundaround end portions of each of these yokes.
 10. The axial-gap motoraccording to claim 1, wherein each of the electromagnet units comprisesa first yoke arranged on one side of the stator frame, straddling onepermanent magnet unit on the rotor frame and having one end opposing thepermanent magnet unit on the stator frame, and a second yoke arranged onthe other side of the stator frame, straddling the permanent magnet uniton the rotor frame and having one end opposing the permanent magnet uniton the stator frame.
 11. The axial-gap motor according to claim 1,wherein the rotor frame has a wall opposing the stator frame and aplurality of grooves made in the wall, extending in the radial directionand provided for holding the permanent magnet units.
 12. The axial-gapmotor according to claim 1, wherein each of the permanent magnet unitshas a magnetic-pole surface which is orientated in an axial direction.13. The axial-gap motor according to claim 1, wherein the permanentmagnets are arranged on the rotor frame in a circumferential direction,with adjacent magnetic poles having the same polarity, differentpolarity or the same polarity and different polarities and spaced apartat regular intervals, irregular intervals or regular and irregularintervals.
 14. The axial-gap motor according to claim 1, wherein thepermanent magnets are arranged on the rotor frame in a circumferentialdirection and in one or more stages, with adjacent magnetic poles havingthe same polarity, different polarity or the same polarity and differentpolarities.
 15. The axial-gap motor according to claim 1, wherein someof the permanent magnet units are arranged on one wall of the rotorframe, which extends in the axial direction, and the remaining permanentmagnet units are arranged on the other wall of the rotor frame, whichextends in the axial direction.
 16. The axial-gap motor according toclaim 1, wherein each of the permanent magnet units comprises a firstpermanent magnet piece arranged on one wall of the rotor frame, whichextends in the axial direction, a second permanent magnet piece arrangedon the other wall of the rotor frame, which extends in the axialdirection, and a third permanent magnet piece arranged between the firstand second permanent magnet pieces.
 17. The axial-gap motor according toclaim 1, wherein at least one part of the rotor frame on which thepermanent magnet units are provided is made of titanium.
 18. Theaxial-gap motor according to claim 1, wherein another rotor frame isprovided on that side of the stator frame which faces away from saidrotor frame, and other electromagnet units are arranged on the otherrotor frame and spaced apart from the permanent magnet units across apredetermined axial gap.
 19. The axial-gap motor according to claim 1,further comprising: a shaft which is coupled to the rotor frame;bearings which support the shaft; and a base in which the bearing areprovided.
 20. The axial-gap motor according to claim 1 or 18, wherein aflywheel is arranged on the rotor frame.
 21. The axial-gap motoraccording to claim 1 or 18, wherein a mechanism is provided to combinethe rotor frame and the shaft together and separate the rotor frame andthe shaft from each other.
 22. The axial-gap motor according to claim20, further comprising a gearbox which change a rotational speed of theshaft.